The present invention relates to display apparatus and more particularly to digitally addressable gas discharge display apparatus.
Digitally addressable gas discharge displays are well known in the art. One form of such apparatus is disclosed by Lustig et al. in their U.S. Pat. No. 3,753,041, and shown in FIGS. 1a and 1b of the drawings which are part of this application. One such apparatus, generally known as a multi-layer display and indicated as 10, comprises a reservoir 11 for establishing a source of ionized gas, a stack of addressing anode electrodes 12, and a plurality of gas discharge display memory cells 13. The electrically conductive members of the display 10 are comprised of any suitable metal and the electrically isolating members are comprised of any suitable insulating material. The display device 10 is adapted to be filled with a suitable ionizable gas such as, for example, "Penning" mixture comprising 99.5% neon and 0.5% argon.
The reservoir 11 is comprised of a cathode plate 14, an electrically insulating spacer shim 15 and an anode plate 16. With the members 14, 15 and 16 assembled, a reservoir is formed which is adapted to contain a portion of the ionizable gas previously described. A suitable source 17 of ionizing potential is connected, through a discharge stabilizing resistor 20, across the cathode 14 and the anode 16. For reference, the anode 16 is connected, for example, to ground potential. A plurality of apertures are disposed through the anode plate 16 forming a matrix configuration. For purposes of illustration only, an 8 by 8 matrix of 64 apertures is shown.
The stack of addressing anodes 12 is comprised of anode plates 21, 22, 23, 24, 25 and 26, each of which has a plurality of apertures therethrough forming a matrix configuration in a manner similar to that described with respect to the plate 16. The number of addressing anodes required is a function of the number of apertures. Interposed between the addressing anodes 21, 22, 23, 24, 25 and 26, are electrical insulators 29, 30, 31, 32 and 33, respectively, each having a matrix of apertures therethrough in a manner similar to that described with respect to the addressing anodes 21-26. Additionally, an apertured insulating plate 34 is interposed between the anode 16 and the addressing electrode 21. Each of the addressing anodes 21-26 is comprised of two electrically conductive portions electrically isolated from each other as shown, one-half of the apertures of each anode plate are disposed through each of the portions respectively. Other anode configurations and orientations are, of course, also possible.
The portions 35-46 are connected to addressing circuits 51 through leads 52-63 respectively. The addressing circuits 51 comprise conventional circuits for selectively applying either a positive or a negative potential to each of the leads 52-63.
The plurality of gas discharge display memory cells 13 are comprised of a cathode plate 70, an electrically insulating plate 71 and a transparent metal film or perforated metal plate anode 72 disposed on the surface 73 of a transparent insulating cover plate 74. The plates 70 and 71 each have a matrix of apertures therethrough in a manner similar to that described with respect to the plate 16. The anode film (if a film is used) 72 comprises any suitable transparent metal film, such as tin oxide, deposited on the surface 73 of the plate 74. Additionally, an apertured insulating plate 69 is interposed between the addressing anode 26 and the cathode plate 70. The plurality of apertures in the cathode plate 70 and the corresponding plurality of apertures in the insulating plate 71 in combination with the anode film 72 form the plurality of gas discharge cells 13. A suitable source 75 of gas discharge sustaining potential is connected across the memory cathode 70 and the memory anode 72.
The anode plate 16, the addressing electrode plates 21-26, the insulating plates 29-34, the insulating plates 69 and 71, and the cathode plate 70 are superimposed or stacked with respect to each other so that the respective matrices or apertures align to form a plurality of gas conductive channels extending from the reservoir 11 to the plurality of gas discharge memory cells 13, respectively. The plate members 14-16, 21-26, 29-34, 69-71 and 74 are contiguously stacked and sealed at the edges thereof to form a gas tight structure. Alternatively, the plate members forming the structure 10 may be mounted inside a gas tight envelope with electrical connections made through gas tight seals in the envelope.
In operation, the gas contained in the reservoir 11 is ionized by the source of potential 17 thus causing a glowing discharge over the surface area of the cathode 14. The gas discharge sustaining potential is applied across the display cells 13 by the source 75. By suitable application by the addressing circuits 51 of positive and negative potential selectively to the portions of the addressing anodes 21-26, a gas discharge column is extended therethrough in a selected channel to emerge from the selected aperture in the anode 26. Ionized gas particles from the excited gas discharge column enter the associated one of the display cells 13 partially ionizing the gas therein and causing ignition thereof by the voltage applied by the source 75. The source 75 maintains the discharge in the selected cell after the discharge column has been extinguished by the removal of the addressing potentials.
A more detailed operation of the display device 10 of FIG. 1 can be had by reference to the specification of the patent to Lustig et al. cited above.
For the apparatus described above to work properly, the cathode plate 14 must be capable of maintaining a gas discharge layer over the entire surface thereof so as to have ionized gas readily available adjacent each aperture and associated gas conductive channel that may be selected by the addressing circuitry 51. In attempting to adapt the basic apparatus of FIGS. 1a and 1b to gas discharge display panels of large area, it was found that, contrary to the required operating conditions, a contiguous layer of ionized gas could not be maintained across the total area of cathode plate 14 except with an attendant high power consumption which is unacceptable for most applications. The absence of such ionized gas adjacent the aperture of an addressed gas conductive channel, of course, causes a non-illumination of the portion of the display associated with the channel, which is also unacceptable.
Various solutions have been suggested for providing the required source of ionized gas on a reliable basis with low power consumption in such larger panels. For example, in the U.S. Pat. No. to Bonn (3,781,599), the basic apparatus of FIG. 1b has the single cathode plate 14 replaced by a plurality of parallel spaced cathode elements disposed within a serpentine path. By applying a potential to the cathode elements in sequence, the ionized gas is made to jump from one cathode element to the next adjacent cathode element thereby creating a shifting motion of the ionized gas discharge across the face of the cathode assembly. As the column of ionized gas, of an area which can maintain a uniform ionized layer at low power consumption, sweeps across the cathode assembly, the addressing circuits are maintained in timed relation with respect to the shifting signals whereby gas discharge columns can be selectively extended in the channels from the glowing stages of the shifting cathode to the display cells thereby ionizing the gas in the selected display cells. This technique is employed in single layer gas discharge displays as well.
Another solution used in both single and multi-layer panels, the series scanning of the total cathode area in segments is, likewise, hampered by limitations -- primarily one of panel address speed. In particular, in a truly "large size" display, the time for serially scanning the total cathode could, conceivably, become a limiting factor. Additionally, the simpler the scanning of the ionized gas reservoir area, the more complex the addressing required to create the desired display. In a truly large display panel the number of addressing anodes, connections thereto, and the attendant addressing logic can also become a limiting factor.
Wherefore, it is the object of the present invention to provide an improved digially addressable gas discharge display apparatus of simple and reliable design capable of use on medium to large multi-layer display panels and also on small to large single layer display panels with low power consumption, minimal external addressing connections and high speed.